Method of making helical coils



Sept. 19, 944.

' o. HAAS MEifIHOD OF MAKING HELICAL poILS Filed July' 9, 1943 ,INVENTOYR w m 0 7% 0M Patented se sis, 1944' UNITED STATES PATENT." OFFICE 1 The present invention relates to helical coils and more particularly coils for iise as screw thread inserts in the boss or nut members oi! screw connections, and aims to provide a' method whereby such coils can be easily produced with great exactness. Hitherto, inserts of the type here in consideration have been wound or coiled of 'a wire. However, it has been found extremely diflicult to produce coils in-whichthe wire crosssection was exactly as desired within narrow that wire coils do not turn out as desired or in suflicient uniformity. On the other hand'jthe' costs of long series or preceding experiments may be prohibitive where the required production isbelow a certain quantity. The invention contemplates therefore to provide a method whereby undesirable stresses tending to deform the ma terial in a more or less uncontrollable manner do not occur or are at least greatly reduced during the production andwhich gives satisfactory results without requiring costly'experiments. The invention mainly consists in that the ,coil is made of a hollow cylinder which first is provided with an-interlor screw threading of a pitch larger than that of the desired coil but with flanks of. the desired shape. The cylinder is then slitted from the outside to the bottom' of the interior thread groove along a helix of a pitch equal to that of said threading so as to produce a coil "of' oversized. pitch which, finally, is reduced to the desired pitch by eompreasionin axial direction. The invention further; consists in that simultaneously with the slitting opera-- tion, the flanks of'the slit-are shaped according to the flanksoi the thread groove inwhich the produced coil is intended to be inserted Further objects and details of the invention will be apparent from the description given hereinafter and the accompanying drawing illustrating the application of'the method and several products thereof by way of example. I

In the drawing. c

Fig. 1 is a cross-section of a nut with a coil insert produced bythemethod according to the invention;

Fig.2isadicillustrationofastep 55 .ofpperation during the production of the coil shown in Fig. i; r

Fig. 3 is a side view partly in section of the finished coil prior. to the insertion in the nut body of Fig. 2; and

Fig. 4 is a diagrammatic illustration similar to Fig. 2 of a coil of a different cross-section oi the convolutions.

Referring now to the drawing, the nut ofv Fig.

' 1 consists of a body I and a thread coil 2; The I body I has a bottom flange 3 projecting inwardly not beyond the threading. A similar. top flange 4 is'formed erterth 2 by 'swaging or turning down the top rim the original form of which is shown in dash lines, upon the top convolution of the inserted-coil. The interior surface 5 of the body is cylindrical. Accordingly, the outer surface of the coil is also cylindrical, and the cross-section of the coil convolutions constitutes in the example of Fig. 1, a rectangular or square base i with a triangle 1 erected thereon so that the sides of the triangle form the flanks of the cpnvolutions of the in terior threadingpf the'hut.

Now, in order to produce the insert2, I first make a cylinder of a diameter equal to the outer diameter of the coil to be produced and preferablyalso-with' shore of a diameter equal to the desired inner diameter of the coil. This is shown in Fig. 2 where a-cylindricai piece 8 is held e. g. by a chuck 9 of'a lathe; and provided with an axial bore. i0. Into cylinder 8 a threading H is cut or tapped the convolutions l! of which. correspond-to the triangles l oi the coil of Fig. 1. However, it will be noticed that the convolutions I! are spaced wider than in Fig. 1 and that the helical groovebetween the convolutions has a narrow straight-lined bottom It. The

cylinder sointeriorly threaded is then slitted 40 from the outside to the groove bottom It in a helix of a pitch equal to that 01' the threading II. In Fig. 2 aportion of the slit is indicated at II and a cutting tool II is shown opposite the bottom It of the thread groove. The cutting edge of the toolhas thesame width as the bottom I: so that the cross-section of the resulting coil convolution "has the same shape as that of the coil Iin Fig. 1. 'Ihefinterlorthreading ll and the helical slit I can be made on the same machine and with the samev lead, so that the desired crow-section can be cut with very great exactness. When the resulting coil is severed from the remainder of the cylinder I it has the shape illustrated in Fig. 3, where the individual convolution: it are spaced from each other ace insertion of thecoil cording to the slit M. The so produced coil has a larger pitch than that shown in the nut of Fig. l and for that reason may be compressed in the axial direction of the arrows a so that the convolutions l6 bear closely upon each other. The'so compressed coil may then be inserted into the nut body I of Fig. 1 and the rim 4 turned down as hereinbelore described. Of course, it is also possible to insert the coil with spaced convolutions into the nut body I and then to compress it and simultaneously turn down the top rim 4. If in this event the coil was originally made with its outer diameter equal to the inner diameter 5 of the nut body I then the compression will tend to expand the coil convolutions with the result that a radial pressure is set up and in consequence also a very appreciable anddesirable friction between the coil and the nut body.

II the nut is intended to be used with a stud having lands between the stud convolutions no axial compression of the coil with spacedconvolutions It may be necessary or only an axial compression or extension in order to make the space H corresponding to the size of said lands of the mentioned stud threading.

In a very similar manner a coil of diamond shape can. be produced which would be useful as an insert into the conventional V-threaded groove of a standard or other nut. This is illus-.

trated in Fig. 4 where first a cylinder 8 is provided with an inner threading ll, triangular inner thread convolutions I2 and groove bottom 13 in the same manner as described with respect to Fig. 2. Instead, however, of a straight-faced cutting tool it a tool it with triangular cutting edge is used in order to cut from the outside to the groove bottom l3. Owing to the triangular shape of the tool the outer faces ll of convolutions 18 of diamond cross-section will be shaped simultaneously with the slitting. In other respects the so produced coil is similar to the coil of Fig. 3. The coil may be compressed in axial direction so that the coil convolutions contact each other or the coil with originally spaced convolutions may be screwed into a conventional female threading whereby an axial compression of the coil will occur owing to the interengaging 1. A method of producing a screw thread insert coil comprising the steps ofmaking a hollow cylinder with an outer diameter according to that of the desired coil, providing the cylinder with an inner helical groove of a flank form according to the'desired screw thread and with a groove bottom of selected width and pitch, slitting the cylinder from the outside to the bottom of said groove along a helix-of a width and pitch equal to that of said groove bottom, severing the so produced coil from the remainder of the cylinder, and compressing it-in axial direction 'to bring the coil convolutions into engagement with each other. v

2. A method of producing a screw thread coil for insertion into the thread groove of an interiorly screw threaded body which comprises making a cylinder of a diameter substantially equal to the bottom diameter of the thread groove of the body for which the coil is destined, providing said cylinder with an inner helical groove of desired flank form and selected pitch and width of its groove bottom, slitting the cylinder from the outside to the bottom of said last mentioned groove along a helix of a pitch equal to said selected pitch and with a width of the slit substantially equal to that of said last mentioned groove bottom, simultaneously shaping the flanks of said slit according to the flanks of the thread groove of the body for which the coil is destined, severing the so produced coil from thev remainder of the cylinder, and changing the selected pitch to that of the threading or said body by subjecting the coil to the action of a force applied in an axial direction.

OTI'O HAAS. 

